Subsurface exploration



Aug. 15, 1961 A. s. MCKAY ET Al.

SUBSURFACE EXPLORATION Filed Jan. 2, 1958 United States Patet 2,996,615 SUBSURFACE EXPLORATION Alexander S. McKay and Edmond F. Egan, Houston,

Tex., assiguors to Texaco Inc., a corporation of Delaware Filed Jan. 2, 1958, Ser. No. 706,763 8 Claims. (Cl. 25043.5)

tion, that is, the formation from which a fluid or fluids, such as oil, Water or gas is or are flowing into the borehole.

In the method of this invention the borehole is provided with a string of tubing extending downwardly at least to the bottom of the producing formation so as to form two channels for conveying borehole fluid to the surface, one channel being through the tubing and the other channel being through the annulus or annular space between the tubing and the well casing or the walls of the borehole.

The flow rates of the fluids passing upwardly through the tubing and the annulus are controlled so that there will be a nullpoint of flow in the annulus within the zone or formation of interest, that is, a point in the annulus where the flow of well fluid divides into two streams, one stream flowing upwardly in the annulus to the surface and the other stream flowing downwardly in the annulus to the tubing throughan opening therein located preferably below the producing formation of interest. The position of this null point or'interface can be moved up or down along the wall of the formation by varying the ratio of;

the flow rates of the two fluids. It is to be understood that one fluid only, for example, oil may be flowing into the borehole from the producing formation of interest or that different fluids such, for example, as oil and gas, water and oil or the like may be flowing from the formation into the borehole. Gas, for example, may be flowing into the borehole from a particular section or sections of the formation while oil flows into the hole from another section or sections. This is to be taken into consideration where reference is made hereinafter to the two fluids flowing upwardly to the surface, one through the tubing and the other through the'annulus. In other words, it is to be understood that these fluids may be the same, that is, both fluids may be oil but flowing into the borehole at diiferent rates from different sections of the formation,

or that the fluid flowing upwardly through the tubing may be, say, oil while the fluid flowing upwardly through the annulus may be gas. The position of the null point is readily determined by introducing at a point within the zone of entry of 'the fluid into the borehole a radioactive tracer material and detecting the presence or absence of the tracer material in one of the two streams, and repeating this operation for other tracer material introductory points.

For a better understanding of the invention reference may be had to the accompanying drawing in which:

- FIG, 1 is a vertical sectional view through a portion of a borehole traversing a producing formation or zone showing the arrangement thereinof apparatus used in accordance with this invention; and

FIG. 2 is a vertical sectional view through a portion of a borehole traversing a permeable formation or zone showing a modification of the apparatus illustrated in FIG. 1.

.at the surface.

ice

- Referring to the drawing, and particularly to FIG. 1 there is shown a borehole 10 traversing a producing formation from whicha fluid such as oil, water or gas is flowing into the borehole. The upper'portion of the borehole 10 is lined with acasing 14 having a closed casing head 16 A string of tubing 18 extends down'- wardly into the borehole to a depth below the formation 12. A first outlet pipe 20 is connected through the casing head 16 to the annular space between the tubing 18 and the casing 14 and this pipe 20 contains a flow meter 22 and a flow controlling valve 24. Likewise an outlet pipe 26 is connected to the interior of the tubing 18 which con-. tains a flow meter 28 and a flow controlling valve 30.. The valves 24 and 30 control respectively the flow rates. of a first fluid 32 which flows upwardly through the annulus between the tubing 18 and the wall of the bore: hole 10 and a second fluid 34 which flows upwardly.

through the tubing 18. Under these conditions there willbe a depth or locationin the annular space at which the flow of fluid entering the borehole 10 divides. Thus the first fluid 32 is shown as entering the borehole 10 from an upper section of the formation 12 and the second fluid 34 as entering the borehole 10 from a lower section.

A null point of fluid flow or an interface between the first and second fluids 32 and 34 thus exists at this depth,

. which is indicated in the figures of the drawing at 36.v This null point 36 can be moved up or down along the wall of the formation 12 by changing the flow rates of the. two fluids 32 and 34 while maintaining constant the sum. of the flow rates of these two fluids.

Thus, merely by way of illustration, the valves 24 and 30 may be first adjusted so that the flow rate of the first fluid 32 is ten gallons per minute while the flow rate' ofthe'second fluid 34 is 20 gallons per minute. It is assumed that with'these flow rates the interface or null point 36 will be in'the position indicated in the figures of the'f drawing. By again adjusting the valves 24 and 30 thei flow rate of the first fluid 32 may be increased to, say, 12. gallons per minute while the flow rate of the secon'djfluid' 34 is'decreased 18 gallons per minute. The total new: rate will remain at 30 gallons per minute but the null point 36 will move downwardly to a somewhat lower position or depth opposite the wall of the formation 12.1. By repeating these operations and measuring the distance, moved by the null'point for each adjustment of the .two' flow rates information will be obtained as to the relative. amounts of the flow of fluids into the borehole from. diiferent vertical sections of the formation 12. I

In this method of measuring the flow rates of the fluids, into the borehole 10 it is of course necesary to locate the; depth or position of the null point 36 for each ratio of the flow rates as controlled by the valves 24 and 30. Thei position of the null point as is readily located by immune" ing a suitable radioactive substance into the fluid as it] enters the borehole ,10 from the formation 12 and their. noting whether or not this radioactive substance passes. upwardly to the surface in the annulus with the first flu'idl 32 or through the tubing 18 with the second fluid 34.

In FIG. la radiation detecting device 38 suitable for; detecting the radioactive substance introduced into thel borehole fluid is shown as suspended within the casing 141 in the annular space between the casing 14 and the tuba, ing.18 on the lower end of a conductor cable 40. This: cable 40 passes over a suitable cable-measuring device 42 which is adapted to measure continuously the length of the cable payed out and thus the depth of the detecting device 38 in the borehole 10. The cable 40 then passesto a recorder 44 which may also contain means for am-fplifying the signals received from the radiation detecting device 38.

A source of radioactive substance 46, for example, a

gamma emitting substance, is suspended from the lower end of the radiation detector 33 and disposed in the annulus at a point in the vicinity of the producing formation 12. When this source 46 is above the null point 36 radioactive material emitted from the source 46 will be carried upward with the first fluid and will be detected by the radiation detecting device 38. As the. source 46 is lowered in step-wise fashion the detecting device will indicate a fairly sharp cut off in the radioactivity in the annular space when the source of radiation substance 46 is lowered beyond the null point since the first fluid 32 within which the detecting device 38 is disposed no longer contains the emitted radiations. Accordingly, it can be seen that an indication of a change in radioactivity is an indication of the null point in the annulus.

To determine the nature of the fluid entering the borehole, the well can be flowed under fixed conditions and samples taken at the surface to measure gas-oil or oilwater ratios from different sections. in the well.

' Although this method has been described in connection with a naturally flowing well is should be understood that this method can also be applied to pumping wells, for example, by utilizing two pumps in the casing 14.

The source of radioactive substance 46 may consist of a solution of sodium iodide 131 enclosed by' a semipermeable membrane so as to continuously release the radioactive substance into the borehole fluid. It could be lowered into the borehole, attached to a separate wire line or attached to the cable 40 connected to the detecting device 38, as well as by being suspended from the detecting device 38, as illustrated in FIG. 1.

FIG. 2 illustrates another arrangement of apparatus which may be used in accordance with the method of this invention. In this arrangement a preferably liquid radioactive substance is stored in a small tank 48 at the surface and introduced into the borehole fluids by means of a pump 50 and a movable string of small tubing, 52 leading to producing formation 12. A detecting device 38a may then be located within the tubing 18, as shown in FIG. 2, or if preferred in the annulus. This detecting device 38a is held stationary at a point in the tubing 18 in the vicinity of the producing formation 12. The location. of the null point is determined by measuring the length of the movable string of small tubing 52 in the annular space. More specifically with the lower end of the small tubing 52 and the radiation detecting device 38a positioned as in FIG. 2, the lower end of the small tubing 52 being disposed above the null point 36, the radioactive substance introduced into the fluid above this null point 36 will flow upwardly with the fluid. Although the detecting device 38a is shown more or less opposite the lower end of the small tubing 52 the detecting device will have a rather low response, since the radiation substance will be scattered in the fluid moving upwardly in the annular space, and therefore away from the radiation detecting device 38a. In other words the presence of the radioactive substance in the fluid outside of the tubing 18 will have very little effect on the radiation detecting device 38a, particularly if a substance is used which gives off soft radiation. However, if then the small tubing 52 is lowered so that its lower end is below the null point 36 the radioactive substance will no longer pass upwardly with the fluid but rather will pass downwardly and into the tubing 18. The detecting device 38a will then be surrounded with the radioactive substance and will therefore show a considerably higher response. By raising or lowering the small tubing 52 by increments and by observing the response of the radiation detecting device 38a after each movement of the small tubing 52 the exact position of the null point 36 can be determined. The arrangement illustrated in FIG. 2 has the advantage that the rate of injection of the radioactive substance into the borehole fluids can be easily controlled.

If desired the small tubing 52 may be maintained in a fixed position and a length of flexible tubing, not shown, attached to the lower end of the small tubing 52. The

4 a position of the open end of the flexible tubing could be adjusted by means of a wire line attached thereto and running to the surface.

If desired the radiation detecting devices 38 and 38a may be disposed at the surface either in the fluid flowing from the first outlet pipe 20 or the second outlet pipe 26. In such a case however there will be a certain lag in response since when the lower end. of the small tubing 52 or the source of radioactive substance 46 passes the null point 36 the tracer will shift from the upwardly flowing fluid 32 to the downwardly flowing fluid 34 or vice versa and since there will be considerable fluid both within the tubing 18 and within the annulus it may be some time before the radioactive substance reaches the surface. It is preferred, therefore, that the radiation detecting device be suspended in the borehole at a point more or less in the vicinity of the producing formation 12.

Although sodium iodide 131 enclosed in a semi-permeable membrane has been mentioned hereinabove as one means of introducing a radioactive substance into the borehole fluid, it should be understood that other radioactive sources, for example, other radioactive iodine compounds, and even other means may be used which will introduce a suitable radioactive tracer material in the fluids. The other means may be, for example, an electrical circuit including an electrode of a well-known type which is both electrically conductive and radioactive. The

electrode, which is disposed in the annulus in the vicinity of the producing formation, may be made of copper or lead in which a radioactive phosphorus has been dissolved. The radioactive phosphorus is released into the borehole fluid at a rate dependent upon the current flow through the electrode. The current flow may be readily controlled by extending the circuit to the surface of the earth. Another radioactive substance which may be used in the electrode is cadmium 115. Regardless of what source is used, it should be free to move up and down within the annulus through a distance at least as great as the thickness of the producing formation that is being logged.

Accordingly, an improved productivity profile logging method has been described which includes producing a null point of flow in a producing well in the annulus about the tubing, moving the point of null flow by changing the flow rates through the tubing and annulus, determining the position of each of the null points with a radiation detector and by noting differences in flow rate.

. Thus, the relative rates of the flow of fluid or fluids through different sections of the wall of a borehole traversing a producing zone when the fluid is flowing from a formation into the borehole may be readily determined. More specifically, the invention provides a method of determining the exact zones from which gas, oil or water is entering a producing well without the necessity of using packers in the well.

Obviously, many other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof but only such limitations should be imposed as are indicated in the appended claims.

'We claim:

1. A method of obtaining a productivity profile log of a producing formation of a well having a tubing therein extending down at least as far as the bottom of said formation which comprises dividing the fluid entering into the well from the producing formation into first and second streams flowing upwardly and downwardly, respectively, in the annulus about said tubing so as to establish in the annulus a null point of flow of the formation fluid at a location within the vertical extent of said formation, introducing a radioactive substance into one of said streams in the annulus at a known depth in the vicinity of said formation, determining the depth of said radioactive substance when said substance is introduced into the other of said two streams and establishing a null point at another location while maintaining the total flow rate constant and repeating these operations While noting the flow rates of the fluid for each location of said null point in at least one of these streams.

2. A method of obtaining a productivity profile log of a producing formation of a well having a tubing therein extending down at least as far as the bottom of said formation which comprises dividing the fluid entering into the well from the producing formation into first and second streams flowing upwardly and downwardly, respectively, in the annulus about said tubing so as to establish in the annulus a null point of flow of the formation fluid at a location within said formation, introducing a radioactive substance into the fluid in the annulus at various known depths in the vicinity of said formation, determining the location of said null point by determining for each of the various known depths the radioactivity in one of said streams and establishing a null point at another location while maintaining the total flow rate constant and repeating these operations while noting the flow rates of the fluid for each location of said null point in at least one of these streams.

3. A method of determining the fluid flow from each of a plurality of difierent sections of a producing formation of a well having a tubing therein extending to a point below said formation which comprises dividing the fluid entering into the well from the producing formation into first and second streams flowing upwardly and downwardly, respectively, in the annulus about said tubing so as to establish in the annulus a null point of flow at a position within said producing formation, introducing a radioactive substance into one of said streams in the annulus at a known depth, determining the stream into which said substance is being introduced, then introducing said substance into said fluid at another depth until said substance is introduced into the other of said two streams, and establishing the null point at another position while maintaining the total flow rate constant and repeating these operations.

4. A method of determining the relative rates of the flow of fluid through sections of the wall of a borehole containing a string of tubing extending down at least as far as the bottom of a producing zone which comprises dividing the fluid entering into the borehole into two streams by controlling the rates of flow of fluid through said tubing and through the annulus between the tubing and the walls of the borehole so that a null point will exist in the annulus within said zone between fluid of one of the two streams flowing in said tubing and the fluid of one of the two streams flowing in the said annulus, introducing a radioactive substance into the fluid in the annulus, measuring the depth in the hole of said nul1 point by determining the radioactivity in one o f said streams, varying the ratio of the flow rates of the streams in the tubing and in the annulus while maintaining constant the sum of the rates of the two streams so as to cause said null point to move along the wall of the borehole to a new position, determining the depth of the null point at said new position and repeating these operations while noting the ratios of the flow rates of the two streams for each measured depth of the null point in the borehole.

5. A method of determining the relative rates of the flow of fluid through sections of the wall of a borehole containing a string of tubing extending down at least as far as the bottom of a producing zone which comprises dividing the fluid entering into the borehole into first and second streams by controlling the rates of flow of fluid through said tubing and through the annulus between the tubing and the walls of the borehole so that a null point will exist in the annulus within said zone between fluid of said first stream flowing in said tubing and the fluid of said second stream flowing in said annulus, introducing at a known depth a radioactive substance into the fluid in the annulus, determining the radioactivity in one of said streams, repeatedly introducing a radioactive substance into the fluid in the annulus at other known depths until a change in the radioactivity in said one stream is determined and varying the ratio of the flow rates of the fluids in the tubing and in the annulus while maintaining constant the sum of the rates of the two fluids so as to cause said null point to move along the wall of the borehole to a new position and repeating these operations while noting the flow rates of the two streams for each measured depth of the null point in the borehole.

6. A method as set forth in claim 5 wherein the radioactivity in said first stream is determined.

7. A method as set forth in claim 5 wherein the radioactivity in said second stream is determined.

8. A method of productivity well logging of a borehole traversing subsurface formations and containing a string of tubing extending down at least as far as the bottom of a zone in which measurements are to be made which comprises regulating the pressure within said borehole to provide for flow of fluid into said borehole from said zone of the formation surrounding the borehole, con trolling the resistance to flow of said fluid both in said tubing and in the annulus between the tubing and the borehole wall so that the flow of fluid from said zone divides into a portion flowing upwardly through said tubing and another portion flowing upwardly through said annulus so as to form a null point in said annulus, measuring the rates of flow of said two fluid streams, introducing a radioactive substance into the fluid in the annulus at various known depths in the vicinity of said zone, determining the location of said null point by determining for each of the various known depths the radioactivity in one of said streams, altering the relative resistances to the rates of flow of said two streams while maintaining the total rate of production constant, again measuring the rates of flow of the two streams and also determining the depth of the null point at its new position resulting from the change in the relative rates of flow of said streams and repeating these operations while noting the ratios of the flow rates of the two fluids for each measured depth of the null point in the borehole.

References (Iited in the file of this patent UNITED STATES PATENTS 2,433,718 Teplitz Dec. 30, 1947 2,700,734 Egan Jan. 25, 1955 2,749,444 Shea June 5, 1956 2,765,412 Scotty Oct. 2, 1956 2,805,346 Piety Sept. 3, 1957 2,835,819 Herzog May 20, 1958 2,868,506 Nestle Jan. 13, 1959 

